The invention relates to speech coding devices and methods, such as for speech recognition systems.
In speech recognition systems, it is known to model utterances of words, phonemes, and parts of phonemes using context-independent or context-dependent acoustic models. Context-dependent acoustic models simulate utterances of words or portions of words in dependence on the words or portions of words uttered before and after. Consequently, context-dependent acoustic models are more accurate than context-independent acoustic models. However, the recognition of an utterance using context-dependent acoustic models requires more computation, and therefore more time, than the recognition of an utterance using context-independent acoustic models.
In speech recognition systems, it is also known to provide a fast acoustic match to quickly select a short list of candidate words, and then to provide a detailed acoustic match to more carefully evaluate each of the candidate words selected by the fast acoustic match. In order to quickly select candidate words, it is known to use context-independent acoustic models in the fast acoustic match. In order to more carefully evaluate each candidate word selected by the fast acoustic match, it is known to use context-dependent acoustic models in the detailed acoustic match.